1. Field of the Invention
The present invention relates to an optical communications system using digital wrapper technology, and to a communication device and a network management device, which are used in the communications system.
2. Description of the Related Art
With an increase in data traffic transmitted/received via a network, network configuration methods (such as SDH/SONET, Ethernet (trademark), etc.) have been diversified in recent years. Additionally, as the scale of a network, a large-scale network where transmission lines as long as several thousands of kilometers are installed, and several tens of communication devices are provided is commercialized. Furthermore, transmission rates differ depending on communication services rendered in many cases. Besides, there is a demand for building a large-scale network where these networks are integrated.
SDH (Synchronous Digital Hierarchy) is a frame format that is standardized internationally. STM-16 of 2.4 Gbits/s, STM-64 of 10 Gbits/s, etc. are recommended based on STM-1 of 156 Mbits/s. Additionally, in the United States, SONET (Synchronous Optical NETwork), which is substantially the same technology as SDH, is a de facto standard. In the meantime, Ethernet is a packet communication method using CSMA/CD (Carrier Sense Multiple Access with Collision Detection) technology, and is widespread throughout the world.
However, in an SDH/SONET communications network, a unique overhead (header information) is added to the beginning of each frame, and a communication between communication nodes is established based on the overhead. Accordingly, a device that cannot process this overhead is unavailable within an SDH/SONET communications network. On the other hand, in an Ethernet network, data is transmitted/received with a packet having a predetermined format. Therefore, a device that cannot process this packet is unavailable within an Ethernet network.
As described above, if networks of different communication methods exist, their configurations become redundant.
As a technology for solving this problem, attention is focused on digital wrapper technology, which is stipulated in ITU-T (International Telecommunication Union Telecommunication standardization sector) G709. The “digital wrapper” is a frame formatting technology for an OTN (Optical Transport Network), and sometimes called “Digital Pipe”. In a digital wrapper network, a signal of any method (an SDH/SONET signal, an Ethernet signal, etc.) is stored in a predetermined format and transmitted. Namely, a signal of any communication method is wrapped with a predetermined format, and transmitted. Details of the description on the digital wrapper technology are disclosed as a publication of ITU-T (for example, see Non-patent Document 1). Besides, as to the technology for storing an SDH frame, etc. in a frame having a different form and for transmitting the frame, a patent application has been already filed (for example, see Patent Document 1).
[Non-patent Document 1]
ITU-T G.709/Y.1331
[Patent Document 1]
Japanese Patent Publication No. 2001-177491 (FIG. 3, paragraphs 0050 to 0055 and 0066).
However, the digital wrapper is a new technology, and its details are currently under study. Accordingly, how to build a network with the digital wrapper technology, or the details of a data structure of an overhead of a digital wrapper frame has not been finalized yet.
Consequently, almost no studies have been made to restore a fault when it occurs on a network built with the digital wrapper technology. Or, almost no studies have been made to enhance the reliability (fault tolerance) of a network built with the digital wrapper technology. Note that the Patent Document 1 provides a function for switching a session by using a newly defined overhead when a fault occurs. With this function, however, only a session is switched by devices existing at both ends of a transmission line on which the fault occurs, and efficient restoration considering an entire network cannot be made.